Selected aspects of fatty acid metabolism, which are considered to have important roles in maturation and differention, will be studied using isolated subpopulations of guinea pig megakaryocytes that are relatively homogeneous in regard to phases of maturation. The enzymatic basis of the observation that de novo fatty acid synthesis occurs primarily in mature megakaryocytes and not in immature megakaryocytes will be studied by both immunologic and radiometric enzyme assays. The two primary enzymes involved in fatty acid synthesis, fatty acid synthase and acetyl-CoA carboxylase, will be assessed using immunologic methods as well as enzymatic determinations on defined subpopulations of megakaryocytes. Correlations between presence of enzyme by either technique and morphologic stage, ploidy and size of cells and protein content will be made. As acylation reactions appear to be altered during megakaryocyte maturation, acetyl transferase activities and CoA-independent and CoA-dependent transacylase activities will be determined on isolated fractions of megakaryocytes. The activity of delta-5 and 6 desaturases, key enzymes in the de novo synthesis of arachidonic acid, will be investigated in megakaryocytes at various stages of maturation to determine whether de novo synthesis of arachidonic acid is more active at specific stages of megakaryocyte maturation. The results of these studies should further define the relationship between fatty acid metabolism and megakaryocyte maturation and provide new information in regard to membrane biogenesis in megakaryocytes.